1. Field of the Invention
This invention relates to a discharge pulsation damping apparatus for a compressor used in a car air conditioner, a compressed air supply apparatus, and so forth.
2. Description of the Related Art
A compressor of this type has a construction in which a compressive fluid sucked from outside is introduced into an operation chamber and the pressure of this compressive fluid is elevated by reducing the volume of the operation chamber. In such a compressor, the compressive fluid so compressed is discharged from the operation chamber into a discharge chamber within a predetermined time interval. In consequence, a so-called "discharge pulsation" occurs due to the pressure change inside the discharge chamber in accordance with the discharge timing. In a reciprocation type compressor in which a plurality of cylinder bores are bored around a rotary shaft and pistons accommodated in the cylinder bores are caused to reciprocate by a rocking motion of a swash plate that is fitted to the rotary shaft to execute the compression operation, a discharge pulsation, that has various orders (ratio of revolutions to frequency) of frequency components corresponding to the number of the cylinder bores (the number of cylinders) occurs. When such a discharge pulsation takes place, resonance occurs in external piping arrangements connected to the compressor, thereby inviting the problems of vibration and noise.
To reduce the vibration and the noise, conventional compressors are equipped with a discharge pulsation damping apparatus that damps the discharge pulsation occurring due to the compression operation of the compressor. An expansion type discharge muffler is known as a discharge pulsation damping apparatus of this kind. The discharge muffler defines an expansion space having a predetermined capacity inside the housing of a compressor, and supplies a compressive fluid from the discharge chamber to the external piping arrangements through the expansion space.
However, the construction according to the prior art generally needs an expansion space having a sufficient capacity so as to effectively damp the discharge pulsation, and this invites an increase in the size of the compressor. In a compressor that is used as a car air conditioner, the mounting space for the compressor, inside the engine compartment, is limited. Therefore, the conventional expansion type muffler cannot secure a sufficient capacity and cannot sufficiently damp those noise components which have a predetermined frequency range in the discharge pulsation.
This problem could be solved, for example, by connecting a resonance type discharge muffler comprising a resonance space like a dead end having a predetermined capacity on an intermediate portion of a discharge passage that extends from the discharge chamber of the compressor to the external piping arrangement, through a communication passage. In the resonance type discharge muffler, a part of the compressive fluid flowing through the discharge passage is guided into the resonance space through the communication passage. A pressure change that offsets the frequency component in a predetermined frequency range in the discharge pulsation is thus generated.
In order to stably generate the pressure change that offsets the intended frequency component, however, the resonance type muffler must always keep the capacity of its resonance space at a predetermined value. However, the compressive fluid contains a lubricant, water, etc, in order to secure lubricating and cooling functions at sliding portions inside the compressor. Quite naturally, therefore, the lubricant, etc, flows with the compressive fluid into the resonance space. When such a lubricant condenses and stays inside the resonance space, the capacity of the resonance space changes. This change makes the generation of the pressure change unstable and eventually, the intended frequency components cannot be damped sufficiently.